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TROPICAL STORM GABRIELLE DISCUSSION NUMBER 20
NATIONAL WEATHER SERVICE MIAMI FL
11 AM EDT SUN SEP 16 2001
AIR FORCE RECON REPORTS AND SATELLITE DATA INDICATE THAT GABRIELLE
HAS BECOME BETTER ORGANIZED THIS MORNING AND HAS STRENGTHENED
SLIGHTLY. A RECON REPORT AT 16/1140Z INDICATED A CENTRAL PRESSURE
DOWN TO 995 MB...WHILE THE 16/1328Z REPORT INDICATED 1500 FT
FLIGHT-LEVEL WINDS OF 67 KT NORTHWEST OF THE CENTER IN DEVELOPING
CONVECTION. THERFORE...THE INTENSITY HAS BEEN INCREASED TO 55 KT
FOR THIS ADVISORY. RECON ALSO INDICATED THE TEMPERATURE IN THE
CENTER HAS WARMED AND SATELLITE IMAGERY INDICATES INCREASING
ANTICYCLONIC OUTFLOW IN THE NORTHWEST SEMICIRCLE...ALL OF WHICH
SUGGEST THAT GABRIELLE IS STILL A WARM-CORE TROPICAL CYCLONE.
THE INITIAL MOTION IS 065/17. THE NHC MODEL GUIDANCE REMAINS IN
EXCELLENT AGREEMENT ON TAKING GABRIELLE TO THE NORTHEAST THROUGHOUT
THE FORECAST PERIOD. THE FORWARD SPEED IS EXPECTED TO DECREASE AS
AN APPROACHING SHORTWAVE TROUGH WEAKENS AND GRADUALLY LIFTS OUT TO
THE NORTHEAST OF THE CYCLONE. THE NEXT TROUGH TO FINALLY PICK UP THE
SYSTEM IS FORECAST TO DROP SOUTHEAST OUT OF THE NORTHERN PLAINS
STATES AND GRADUALLY ACCELERATE GABRIELLE TO THE NORTHEAST. THE
OFFICIAL FOREACST IS JUST AN UPDATE OF THE PREVIOUS FORECAST TRACK
AND IS CLOSE TO THE AVN-UKMET-NOGAPS MODEL ENSEMBLE AVERAGE.
SURFACE ANALYSES OVER THE PAST 24 HOURS INDICATE THAT THE COLD HIGH
PRESSURE SYSTEM OVER THE NORTHERN U.S. HAS WEAKENED CONSIDERABLY AND
THAT THE COLD FRONT TO THE NORTHWEST OF GABRIELLE HAS MADE LITTLE
PROGRESS TO THE SOUTHEAST. IT IS QUITE POSSIBLE THAT THE CYCLONE
MAY STAY ON THE WARM SIDE OF THE FRONTAL BOUNDARY AND REMAIN MORE
TROPICAL-LIKE FOR THE NEXT 24 TO 36 HOURS...UNTIL THE NEXT SHORTWAVE
TROUGH FINALLY PICKS UP THE SYSTEM AND MAKES GABRIELLE MORE
BAROCLINIC...OR AT LEAST SUBTROPICAL IN NATURE. UNLESS DEEP
CONVECTION DEVELOPS DIRECTLY OVER THE CENTER...LITTLE ADDITIONAL
INTENSIFICATION SHOULD OCCUR. THERE IS LESS DRY AIR SURROUNDING THE
SYSTEM TODAY...SO MORE CONVECTIVE DEVELOPMENT IS A POSSIBILITY.
FORECASTER STEWART
FORECAST POSITIONS AND MAX WINDS
INITIAL 16/1500Z 31.9N 74.1W 55 KTS
12HR VT 17/0000Z 32.7N 71.5W 55 KTS...BECOMING EXTRATROPICAL
24HR VT 17/1200Z 33.9N 68.2W 50 KTS...EXTRATROPICAL
36HR VT 18/0000Z 35.3N 65.5W 50 KTS...EXTRATROPICAL
48HR VT 18/1200Z 36.7N 63.3W 50 KTS...EXTRATROPICAL
72HR VT 19/1200Z 40.0N 57.0W 50 KTS...EXTRATROPICAL
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